No, it’s not in one of those public auto-checkable thingies (I need to get around to doing this as well as getting it signed by others), but a public key IS available.
After you download it, go System -> Administration -> Software Sources.
Click the Authentication tab. Click Import Key File, select nighton_key.asc from wherever you downloaded it to. After that, you should stop getting any error messages about the lack of a key.
Alternatively, you can use this quick one-liner in a terminal:
wget -q http://www.nighton.net/nighton_key.asc -O- | sudo apt-key add - && sudo apt-get update
Hope that helps!
(This was brought to my attention by a blog post from Andre Gondim.)